The Environmental Protection Agency’s recent weakening of an upcoming rule reducing emissions from power plants provides some relief for Texas utilities but still doesn’t guarantee the prevention of electricity blackouts, the state’s members of Congress alleged today.

The EPA had reduced Texas’ required emissions reduction under the Cross-State Air Pollution Rule, which will require power plants in 27 states to reduce soot- and smog-forming emissions that can travel to downwind states starting Jan. 1. Thirty-one of Texas’ 32 members of Congress said today that “though any relief is helpful,” flawed assumptions incorporated in the rule caused the agency to overestimate how much extra electricity the state grid operator can provide beyond what’s demanded.

The alleged errors highlight the grid operator’s warning recently that the rule “would have resulted in capacity shortages in Texas if the rule were in place this past summer,” the members wrote in a letter to EPA Administrator Lisa Jackson. “EPA must correct this glaring error to ensure that CSAPR does not cause blackouts in Texas.”

The EPA said in a statement that its analysis “shows that Texas power plants can meet this rule’s emission reduction obligations while maintaining a healthy annual capacity reserve margin.”

The single delegation member who didn’t sign the letter, Democrat Lloyd Doggett of Austin, said he supports continued discussion with the EPA on how to protect public health while meeting energy needs. “The final decision should be based upon sound science, not upon ignoring respiratory harm from dirty air, especially to children and seniors,” Doggett said in a prepared statement.

Texas members of Congress including Republican Reps. Joe Barton of Ennis and Michael Burgess of Lewisville, have grilled EPA officials on Capitol Hill regarding the state’s inclusion in the rule and whether it could force power-plant closures, cost the state jobs and cause blackouts. Some Texans have alleged that the agency included the state in the full rule at the last minute and did so on the basis of flawed science.

The state of Texas made that argument in asking a federal appeals court last month to block the rule. The suit alleges that the EPA failed to give Texas full opportunity comment on the rule and that the state’s inclusion was based on calculations made at a single receptor hundreds of miles away in Madison County, Ill.

Dallas-based Luminant Generation Co., Texas’ largest electric utility, announced last month it would shut down two units at a coal-fired power plant because of the rule. EPA has said it tried to work with Luminant to stave off the plant shutdowns.

The upcoming rule won’t cause the predicted blackouts or service disruptions in large part because utilities have until March 2013 to comply with their choice of technologies, Assistant Administrator Gina McCarthy told Congress in September. She defended the agency’s inclusion of Texas as based on sound science and also said the agency gave enough opportunity for Texas officials and utilities to comment.

Analysts have said they think Luminant can install technology, change fuels and buy emissions permits to comply with the rule instead of closing down plants, but the company said there was no guarantee there would be enough allowances available in 2012 in the emissions-trading market that is part of the new rule.

EPA’s proposed changes, which would also relax a cap on how many emission credits can be traded between states in the rule’s first two years, are “a step forward,” the company said recently, adding that it would analyze the agency’s plan.